This month, we learn that there’s more to a person’s beliefs than just one big blob of information! Seth Yalcin (University of California, Berkeley) sits down with us to talk about how a person’s beliefs are sorted into answers to various questions. Click here to listen to our conversation.

According to an influential picture of what a person’s belief state is–one that comes from philosophers like Jaakko Hintikka, David Lewis, and Robert Stalnaker–everything you believe can be encoded as a set of possible situations. Which set of possible situations? The ones that you’re still choosing between, based on the limited information you have. Things could either be this way, or this way, or that way… Then, when you learn something new, you rule some of those possible situations out. Believing more means shortening the list of possible situations you could (according to you) be in right now.

This account of belief has proved quite useful for a lot of purposes, and it’s pretty straightforward to work up into a nice, simple, formal mathematical theory. But there’s a problem! If all your beliefs were just a blob of possible situations, that would mean you’d also believe all the logical consequences of what we would have thought your beliefs were. This means the account makes some odd predictions. For example, it makes the prediction that if William III of England thought he could avoid war with France, he must also have thought he could avoid nuclear war with France. Obviously that can’t be, because William III had no idea about nuclear weapons. But ‘England can avoid nuclear war with France’ does logically follow from ‘England can avoid war with France’–there seems to be no way around that. So what do we do?

Our guest this month proposes that our beliefs don’t just sit there in our minds as one big blob. Rather, they’re organized into sections. Each section is a particular question, and all the beliefs we have in each section are a bunch of answers to that particular question. If we think of belief in that way, then we aren’t committed to William III believing he can avoid nuclear war with France, because he could only believe that if the question who he was at risk of going to nuclear war with was something that could have occurred to him.

Join us as our guest walks us through this fascinating new topic!Matt Teichman